OpaR Controls the Metabolism of c-di-GMP in .

, the leading cause of seafood-associated gastroenteritis worldwide, has a strong ability to form biofilms on surfaces. Quorum sensing (QS) is a process widely used by bacteria to communicate with each other and control gene expression the secretion and detection of autoinducers. OpaR is the master QS regulator of operating under high cell density (HCD). OpaR regulation of biofilm formation has been reported, but the regulatory mechanisms are still not fully understood. bis-(3'-5')-cyclic di-GMP (c-di-GMP) is an omnipresent intracellular second messenger that regulates diverse behaviors of bacteria including activation of biofilm formation. In this work, we showed that OpaR repressed biofilm formation and decreased the intracellular concentration of c-di-GMP in RIMD2210633. The OpaR box-like sequences were detected within the regulatory DNA regions of , , VP0117, VPA0198, VPA1176, VP0699, and VP2979, encoding a group of GGDEF and/or EAL-type proteins. The results of qPCR, LacZ fusion, EMSA, and DNase I footprinting assays demonstrated that OpaR bound to the upstream DNA regions of , VP0117, VPA0198, VPA1176, and VP0699 to repress their transcription, whereas it positively and directly regulated the transcription of and VP2979. Thus, transcriptional regulation of these genes by OpaR led directly to changes in the intracellular concentration of c-di-GMP. The direct association between QS and c-di-GMP metabolism in RIMD2210633 would be conducive to precise control of gene transcription and bacterial behaviors such as biofilm formation.